This invention relates generally to control sytems and more particularly to automated systems for introducing chemicals into water or other liquid treatment systems.
In the copending U.S. patent application Ser. No. 06/607,368, filed on May 7, 1984, and entitled Computerized System For Feeding Chemicals Into Water Treatment System, which has been assigned to the same assignee as the subject invention, and whose disclosure is incorporated by reference herein, there is shown and claimed a system suitable for introducing a desired amount of liquid chemicals into a water treatment, e.g., cooling tower, system under automated, computer control. A summary of that invention is set forth in considerable detail later herein. Suffice for now to state that while the invention of that application is suitable for its intended purposes it may not be suitable for certain small scale water treatment applications. Moreover the system of that invention makes use of electrically operated pumps, such as pulsating pumps, to inject the chemicals into the water treatment system under the control of the computer. In some applications it may be desirable to introduce the chemicals under gravity feed.
Heretofore gravity feed systems have been utilized for providing treatment chemicals into liquid systems, however such prior art gravity feed systems have been generally confined to batch processing, thereby rendering those systems of limited utility. For example in U.S. Pat. No. 4,436,148 (Maxwell) there is disclosed a batch processing system for providing various treatment chemicals to be added to treat petroleum products in or from an oil well or to add treatment chemicals into a water treatment system. In that system valves are controlled to feed treatment liquids to an oil well under only system pressure. In particular the chemical treatment liquid is stored in a drum above a volume chamber. The chamber includes five lines connected to it, each with a valve. A feed line with a feed valve connects the volume chamber to the treatment drum. A vent line with vent valve vents the top of the volume chamber to the atmosphere. A liquid pressure line with a pressure valve connects the flow line to the volume chamber. A flush line with a flush valve connects the bottom of the volume chamber to the well annulus. A gas line with a gas valve connects the volume chamber to the annulus. When the vent valve and the feed valve are open and the other valves are closed, the volume chamber fills with liquid by gravity from the chemicals within the treatment drum. When the pressure valve and the flush valve are open the treatment chemicals which have been measured into the volume chamber are flushed by the produced fluids within the flow line back into to the annulus of the oil well. Thereafter the opening of the flush valve and the gas valve with the concommitant closing of the other valves purges the volume chamber of all liquids, thereby returning it to the condition to be filled again.
While the system of the Maxwell patent is generally suitable for its intended purposes of providing chemicals without the need for pumps, it nevertheless leaves much to be desired from the standpoint of effectiveness. In this regard the system of the Maxwell patent is incapable of precise chemical introduction control since the volume chamber cannot be partially filled (one must introduce the full quantity of chemicals from the tank into the volume chamber). Thus, with the system of the Maxwell patent one cannot adjust the precise introduction of very small quantities of treatment liquids or provide treatment liquids on a continuous basis. Moreover the Maxwell system does not lend itself to automatic measurement of content of the liquid in the tank via measured head pressures.